The present invention relates to the measurement of the ion implant dose in a material, such as a semiconductor material.
Knowing the actual ion implant dose in a material may be advantageous in the manufacture of various products, such as to test process variation, improve yield, monitor product quality, etc. The ability to measure ion implant dose may also be advantageous in the design of new products and systems, such as in the development of semiconductor-on-insulator (SOI) structures.
The ways to produce SOI structures include ion-implantation methods, such as those disclosed in U.S. Pat. No. 7,176,528. Such steps include: (i) exposing a silicon wafer surface to hydrogen ion implantation to create a bonding surface; (ii) bringing the bonding surface of the wafer into contact with a glass substrate; (iii) applying pressure, temperature and voltage to the wafer and the glass substrate to facilitate bonding therebetween; (iv) cooling the structure to a common temperature; and (v) separating the glass substrate and a thin layer of silicon from the silicon wafer.
In order to develop and/or manufacture such SOI structures, it may be desirable to measure the actual ion implant dose of the donor semiconductor (e.g., silicon) wafer. There are a number of existing techniques to obtain an indication of ion implant dose. For example, Secondary Ion Mass Spectrometry (SIMS) is a technique used in materials science and surface science to analyze the composition of solid surfaces and thin films by sputtering the surface of the specimen with a focused primary ion beam and collecting and analyzing ejected secondary ions. These secondary ions are measured with a mass spectrometer to determine the elemental, isotopic, or molecular composition of the surface. SIMS is not a completely adequate approach at least because it is a destructive test and measures only a small area of the sample.
Alternative approaches include in-situ dose monitors, which are used inside the implanter apparatus. Such in-situ dose monitors are also inadequate because they only provide an average ion dose that is presumed to have been implanted. In-situ dose monitors, however, do not measure or compute actual dose in the sample and they are not capable of detecting any non-uniformity or other variations in the implant dose across the sample. An existing implanter equipment manufacturer has developed a measurement and mapping tool based on a single wavelength or narrow wavelength range reflectivity measurement. Such a system is described in U.S. Patent Application Publication No. 2005/0112853, however, the system requires a baseline measurement before implant, which is undesirable. A further alternative approach employs a four-point probe to extract dose information based on resistivity measurements. The measurements, however, are affected by material resistivity, which can vary greatly, and are considered destructive due to the fact that the process requires contacting the sample with the probe.
Several carrier illumination techniques have been described for measurement of dopant profiles after ion implantation during semiconductor processing for making integrated circuits. However, these techniques use pulsed laser illumination (single wavelength) to create carriers and separate probe beams to measure reflectivity. Thus, in most cases such techniques are unable to distinguish between variations in implant dose and implant energy.
For the reasons discussed above, none of the aforementioned techniques and processes for measuring ion implant dose has been satisfactory, such as in the context of manufacturing SOI structures. Thus, there is a need in the art for new methods and apparatus for measuring ion implant dose.